Research options thoroughly
What year/model boat do you have? Assuming it's a Yanmar, there are many options for rebuilding. I took mine out myself (with my dad's help, and I am no mechanic) and had a local guy rebuild it. The local guy was a BIG MISTAKE. In hindsight, I should have shipped it to Mack Boring and had them redo it. Tranny is surprising light and could be easily shipped. I had talked to Mack Boring but thought the shipping would be a hassle. It would not have been; the turnaround would have been much quicker, and my confidence in the workmanship would have been much higher now. FYI - My regular mech said it would be a huge job to pull the tranny ($$$), and wanted to replace it with a new one ($$$). After digging into, talking to some people, I realized that he was thinking of another model of tranny which is, in fact, difficult to pull. Mine was very easy to pull off after removing 8 bolts. So I gave it a shot myself. Figured that if it did not work, he could say "I told you so", charge me accordingly and I would feel better about paying it. FYI - I once docked next to a cruising couple on a small sailboat. Watched the guy pull his out one moring (1 cylinder diesel), rebuild it and put it back in that afternoon. They left for the Carribean the next day.
